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My (basic) understanding of lenses is that their refraction is largely determined by the material (index of refraction) and shape.

It seems possible to make lenses out of deformable materials, which I assume you can change the shape/curvature to change the lens behavior.

My question is are there lens materials that changing their stress/strain/density/mechanical deformation without changing their outer shape can change lens behavior?

Apologies if this is badly worded, and I'm open to suggestions for better framings. I'm pretty new to this.

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    $\begingroup$ How do you produce a mechanical deformation without changing shape? $\endgroup$ – nasu Feb 9 '17 at 20:19
  • $\begingroup$ @nasu Which also raises the question, are stress and strain not just ways to describe mechanisms of mechanical deformation? $\endgroup$ – JMac Feb 9 '17 at 21:21
  • $\begingroup$ Did you mean to ask if there are materials which can change their optical lensing characteristics without going through a change in shape (though not necessarily without movement on the interior)? $\endgroup$ – JMac Feb 9 '17 at 21:21
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    $\begingroup$ key word: "stress-induced birefringence". $\endgroup$ – The Photon Feb 10 '17 at 1:39
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It is possible (by propogating sound waves into a solid, for example) to create internal stress and change optical properties. These changes are rather subtle, however polarized light reveals strain. Other than some concern on the part of lens manufacturers (the presence of internal strains can lower the quality of the image) this does not have many imaging applications.

The color fringes seen in stressed plastic indicate refraction changes on the order of a part per million in the refractive index.

That's not effective in making a lens, but it suffices for building a grating, and acousto-optic modulators are possible with interesting properties.

While it is not mentioned in the question, a strong electric field can change the refraction of a material (solid, liquid, or gas), and much work on Kerr and Pockels effect is done in order to switch and steer laser beams.

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